LONDON — They had rehearsed the piece only once, but already the musicians at the Bavarian Radio Symphony Orchestra were suffering. Their ears were ringing. Heads throbbed.

Tests showed that the average noise level in the orchestra during the piece, “State of Siege,” by the composer Dror Feiler, was 97.4 decibels, just below the level of a pneumatic drill and a violation of new European noise-at-work limits. Playing more softly or wearing noise-muffling headphones were rejected as unworkable.

So instead of having its world premiere on April 4, the piece was dropped. “I had no choice,” said Trygve Nordwall, the orchestra’s manager. “The decision was not made artistically; it was made for the protection of the players.”

The cancellation is, so far, probably the most extreme consequence of the new law, which requires employers in Europe to limit workers’ exposure to potentially damaging noise and which took effect for the entertainment industry this month.

But across Europe, musicians are being asked to wear decibel-measuring devices and to sit behind see-through antinoise screens. Companies are altering their repertories. And conductors are reconsidering the definition of “fortissimo.”

Alan Garner, an oboist and English horn player who is the chairman of the players’ committee at the Royal Opera House, said that he and his colleagues had been told that they would have to wear earplugs during entire three-hour rehearsals and performances.

“It’s like saying to a racing-car driver that they have to wear a blindfold,” he said.

Already there are signs that the law is altering not only the relationship between classical musicians and their employers, but also between musicians and the works they produce.

“The noise regulations were written for factory workers or construction workers, where the noise comes from an external source, and to limit the exposure is relatively straightforward,” said Mark Pemberton, the director of the Association of British Orchestras. “But the problem is that musicians create the noise themselves.”

Rock musicians have talked openly about loud music and ear protection for years. The issue is more delicate for classical musicians, who have been reluctant to accept that their profession can lead to hearing loss, even though studies have shown that to be the case. At the same time, complying with the law — which concerns musicians’, not audiences’, noise exposure — is complicated.

One problem is that different musicians are exposed to different levels of noise depending on their instruments, the concert hall, where they sit in an orchestra and the fluctuations of the piece they are playing. In Britain, big orchestras now routinely measure the decibel levels of various areas to see which musicians are subject to the most noise, and when.

Orchestras are also installing noise-absorbing panels and placing antinoise screens at strategic places, like in front of the brass section, to force the noise over the heads of other players.

“You have to tilt them in such a way so that the noise doesn’t come back and hit the person straight in the face, because that can cause just as much damage,” said Philip Turbett, the orchestra manager for the English National Opera.

They are also trying to put more space between musicians, and rotating them in and out of the noisiest seats.

At the Royal Opera House, the management has devised a computer program that calculates individual weekly noise exposure by cross-referencing such factors as the member’s schedule and the pieces being played.

Musicians are spacing out rehearsals and playing more softly when they can. As the Welsh National Opera prepared for the premiere of James MacMillan’s loud opera, “The Sacrifice,” last year, the brass and percussion sections were told to take it easy at times in rehearsal to protect the ears of themselves and their colleagues, said Peter Harrap, the orchestra and chorus director.

Conductors are also being asked to reconsider their habit of “going for a big loud orchestration,” said Chris Clark, the orchestra operations manager at the Royal Opera House. Composers, too, are being asked to keep the noise issue in mind.

“Composers should bear in mind that they are dealing with people who are alive, and not machines,” said Mr. Nordwall of the Bavarian orchestra.

And companies are examining their repertories with the aim of interspersing loud pieces — Mahler’s symphonies, for instance — with quieter ones. They are also buying a lot of high-tech earplugs, which are molded to players’ ears and cost about $300 a pair. Many orchestras now ask their musicians to put the earplugs in during the loud parts of a performance.

“I have a computer program that gives me a minute-by-minute timeline chart through the whole piece,” said Mr. Turbett of the English National Opera. “I can go back to the musicians and say, ‘Between bar 100 and bar 200, there’s a very loud passage, so please put in hearing protection.’ ”

But these remedies can bring problems. Some musicians in the brass and percussion sections resent being screened off from their colleagues, as if they were being ostracized. Musicians, even if they accept the need to use earplugs occasionally, tend to hate wearing them.

Mr. Garner, the Royal Opera House oboist, said: “I’ve spent nearly 30 years in music and I know all about noise, and occasionally, if I’m not playing and there’s a loud bit next to me, I might shove my fingers in my ears for a few bars. But I have yet to find a musician who says they can wear earplugs and still play at the same level of quality.”

The modern noise-level-conscious orchestra is also dependent, of course, on the indulgence of the conductor. Arriving at an orchestra to find that decisions have been based solely on musicians’ noise exposure can be galling to the sort of conductor who likes to be in control, which is most of them.

Although Switzerland is outside the European Union, an extraordinary noise-related argument between the conductor and the Bern Symphony Orchestra disrupted the opening night of Alban Berg’s “Wozzeck” in March.

The piece called for 30 string players and 30 wind and percussion players, all crammed into a too-small pit. When the stage director complained in rehearsals that the music was too loud, the conductor didn’t order the orchestra to play more softly, but instead asked for a cover over the orchestral pit to contain the noise, said Marianne Käch, the orchestra’s executive director.

That meant the noise bounced back at the musicians, bringing the level to 120 decibels in the brass section, similar to the levels in front of a speaker in a rock concert. The musicians complained. The conductor held firm. But when the piece began, “the orchestra decided to play softer anyway in order to protect themselves,” Ms. Käch said.

That made the conductor so angry that he walked off after 10 minutes or so, Ms. Käch said. Told that there had been “musical differences” between the conductor and the orchestra, the perplexed audience had to wait for the two sides to hash it out.

In the end, the orchestra agreed to return and finish the performance at the loud levels. For subsequent performances, a foam cover that absorbed instead of reflecting the sound was placed above the pit, and the conductor agreed to tone things down.

“This is the problem you find in many places, that the conductors are conducting more and more loudly,” Ms. Käch said. “I know conductors who have hundreds of shades of fortissimo, but not many in the lower levels. Maybe the whole world is just becoming louder.”